I had the same issue, the "rxjs": "^6.0.0" to "rxjs": "6.0.0" didn't work. I had to update my angular CLI to last stable npm install -g @angular/cli and regenerate the project again.
My config now is :
Angular CLI: 7.3.6
Node: 10.15.3
OS: win32 x64
Angular: 7.2.9